It is well known that users respectively use terminals, such as a handy terminal, to communicate with each other. In such a case, a terminal identifier to identify its user is initially assigned to each terminal. Each terminal transmits the terminal identifier through a wireless network. As shown in FIG. 1, if a plurality of users holding the terminal approaches each other, each terminal receives the terminal identifier from the other terminals. In FIG. 1, three users can communicate with each other through their respective terminals and the three terminals form a group by wireless network.
In general, in case of multicast transmission to a plurality of terminals through wireless network, a group identifier such as class D of the IP (Internet Protocol) is assigned to a packet header as destination address. FIG. 2 is a block diagram of a multicast communication apparatus (the handy terminal) according to first example of the prior art. In FIG. 2, when the destination address (destination group) is designated by a user information processing section 300, a sending information generation section 320 retrieves the group identifier of the destination group from a terminal information memory section 340. The group identifier is attached to communication sentence as packet header and transmitted through a sending section 350. On the other hand, in the receiving side terminal, a receiving information discrimination section 330 decides whether the group identifier includes the receiving side terminal in order to decide that the receiving packet is addressed to the receiving side terminal. However, in an environment in which a network component is dynamically changed (network unity and network splits occur) or participating terminals of the group are frequently changed, negotiation to reset the group identifier is necessary whenever a group component is changed. Therefore, the above-mentioned method is unsuitable.
As another method for multicast transmission to a plurality of terminals through a wireless network, a multicast address is calculated by the terminal identifiers of the destination terminals. The multicast address is attached to the communication sentence as a packet header and transmitted. In the receiving side terminal, the packet is determined to be addressed to the receiving side terminal by comparing the multicast address with the terminal identifier of the receiving side terminal. FIG. 3 is a block diagram of the multicast communication apparatus according to a second example of the prior art. In FIG. 3, when the destination address (destination terminal) is designated by the user information processing section 300, the sending information generation section 320 calculates the multicast address according to the terminal identifiers of each destination terminal stored in the terminal information memory section 340. The multicast address is attached to a communication sentence as a packet header and transmitted through the sending section 350. On the other hand, in the receiving side terminal, the terminal identifier of the receiving side terminal is compared with the multicast address of the packet header in order to determine whether the receiving packet is addressed to the receiving side terminal. This method is effective to decide the destination address of the receiving packet. However, if the receiving side terminal belongs to a plurality of groups, and the receiving packet is addressed to the receiving side terminal, it is impossible for the receiving side terminal to identify group to which the receiving packet is transmitted.
In order to solve this problem, it is considered that the host application program includes a function to identify the group in which the receiving packet is transmitted. However, even if the group to which the receiving packet is transmitted does not exist in the network, the receiving packet will be supplied to the host application program in the receiving terminal. The host application program must then execute processing for the receiving packet, the processing for which is unnecessary, and the processing efficiency for all communication software decreases.
Furthermore, if the destination group of the receiving packet is not identified by the group management section 302, the packet is not received when group components are changed. For example, assume that three terminals A, B, C form one group, and negotiation for another terminal X to participate in the group is executed among the terminals A, B, C. When negotiation from the terminal X to the terminal A is completed and negotiation from the termanal X to the terminals B and C is not completed, the terminals B and C cannot receive the packet sent by terminal A. Therefore, communication efficiency decreases. In order to solve this problem, it is necessay to inform all group components (the terminals A, B, C) of the change. However, in this case, processing efficiency decreases.
In short, in order to set a unique group identifier on a wireless network, negotiation is first executed among all participating terminals of the group, or a fixed group identifier is set under management of a server. In the distributed environment in which the group component is frequently changed, negotiation is necessary whenever the group component is changed and the communication traffic increases.